Originally Posted by
7milesout
Precision - I would love a 6th gear. However I think the mpg return for a 6th gear would realize minimal gains. And there wouldn't be enough sales of that transmission because the U.S. is one of the higher speed countries. These things you may know already, I do feel like I'm preaching to the choir.
One of the things I have complained about is the gap from 1st to 2nd. I mentioned my first impression was that 2nd gear was too tall. But since I'm an engineer and I sit around and do nerd engineering crap, I charted out our gear spacing. Turns out, 2nd gear is fine ... first gear is too short.
The below graph is road speed vs. rpm per gear. It is accurate. The multi-colored lines are gears 1 through 5. The horizontal dashed and vertical down arrows represent shifting from one gear to the next so that the next gear becomes active at 2,500 rpm. 2,500 rpm is where I feel from where the engine pulls nicely, just regular cruising acceleration. Not "racing," and not absolute mpg focused, just comfortable.
As you can see, we have to rev the manure out of it in 1st gear (4,600 rpm), to make the switch and hit 2,500 rpm in 2nd. I DO NOT LIKE THAT. I'd rather it be more like 3,750 rpm in first, and switch to 2nd and hit 2,500 rpm.
But the rest of the gear changes are very reasonable. 3,637 rpm, 3,375 rpm and 3,000 rpm. A 6th gear would be nice, but I doubt we'd ever see it. It turns out that shifting to 2nd @ 20, 3rd @ 30, 4th @ 40 and 5th @ 50 is really close to the chart below based on the grid lines and horizontal axis being mph.
...
I also plotted out the actual hp / tq chart, because the only ones I've seen posted on the site are wrong. It is for the 74 hp engine, but good enough for the 78 hp engine as well. I used it to determine the road speeds for shifting to achieve the quickest acceleration. Basically the shift points that would lead to the lowest drag strip times ... even though it may be just fractions of a second quicker than hitting redline each time. I was going to decal my speedo at the quickest acceleration shift points, but the lens cover is so curved away from the speedo, it is difficult to place it and make it look correct. Anywho - I do lots of nerd engineering crap like that.